Device emitting or detecting terahertz waves, and manufacturing method for device

ABSTRACT

A device, comprising: an antenna array provided with a plurality of antennas each having a semiconductor layer having terahertz-wave gain; and a coupling line for mutual frequency-locking of at least two of the antennas at a frequency of the terahertz-wave, wherein the coupling line is connected to a shunt device, and the shunt device is connected in parallel to the semiconductor layer of each of the two antennas.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a device that emits or detectsterahertz waves, and to a manufacturing method for the device.

Description of the Related Art

There is known an oscillator, in which a resonator and a semiconductordevice having terahertz electromagnetic-wave gain are integrated, as acurrent-injection type light source that generates terahertz waves,which are electromagnetic waves in a frequency region of at least 30 GHzand not more than 30 THz. Particularly, there is expectancy for anoscillator, in which a resonant tunneling diode (RTD) and an antenna areintegrated, as a device that operates at a frequency region near 1 THzat room temperature.

“Jpn. J. Appl. Phys., Vol. 47, No. 6 (2008), pp. 4375-4384” describes aterahertz-wave oscillator in which an RTD and a slot-antenna resonatorare integrated on a semiconductor substrate. In this description, adouble-barrier RTD made up of an InGaAs quantum-well layer and AlAstunnel-barrier layer epitaxially grown on an InP substrate is used. Anoscillator using such an RTD can realize terahertz-wave oscillation in aregion, where voltage-current (V-I) characteristics yield negativedifferential resistance, at room temperature.

Further, Japanese Patent Application Publication No. 2014-200065describes a terahertz-wave antenna array in which a plurality ofoscillators, in which RTDs and antennas are integrated, are arranged onthe same substrate. The antenna array described in Japanese PatentApplication Publication No. 2014-200065 is capable of increasing antennagain and power, by adjacent antennas synchronizing with each other.

“IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 42, NO. 4,APRIL 1994” describes a configuration where adjacent antennas areconnected by a chip resistor to achieve mode stabilization.

However, increasing the number of antennas (the number ofnegative-resistance devices) in the antenna array increases the numberof modes to be synchronized (number of resonance frequency bands),hence, the greater the number of antennas is, the more difficultstabilization of generation or detection of terahertz waves by thedevice becomes.

Accordingly, there have been cases in devices having a plurality ofantennas where efficient generation or detection of terahertz waves isnot realized due to there being a plurality of modes forsynchronization.

SUMMARY OF THE INVENTION

Accordingly, the present technology realizes more efficient generationor detection of terahertz waves in a device provided with a plurality ofantennas.

A first aspect of the disclosure of the present technology is:

a device, comprising:

an antenna array provided with a plurality of antennas each having asemiconductor layer having terahertz-wave gain; and

a coupling line for mutual frequency-locking of at least two of theantennas at a frequency of the terahertz-wave, wherein

the coupling line is connected to a shunt device, and

the shunt device is connected in parallel to the semiconductor layer ofeach of the two antennas.

A second aspect of the disclosure of the present technology is:

a manufacturing method for a device provided with an antenna arrayhaving a plurality of antennas, the method comprising:

forming, on a substrate, a semiconductor layer having terahertz-wavegain;

forming, on the substrate, a first conductor layer;

forming a shunt device connected in parallel to a semiconductor layer ofeach of two antennas, and connected to a coupling line for mutualfrequency-locking of the plurality of antennas at the terahertz-wavefrequency; and

forming a third conductor layer to form the coupling line that has astructure where a first dielectric layer is sandwiched between the firstconductor layer and the third conductor layer.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are diagrams illustrating equivalent circuits of asemiconductor device according to a first embodiment;

FIGS. 2A through 2C are diagrams illustrating a configuration of thesemiconductor device according to the first embodiment;

FIG. 3 is a diagram illustrating impedance of the semiconductor deviceaccording to the first embodiment;

FIGS. 4A through 4C are diagrams illustrating a configuration of asemiconductor device according to a first modification; and

FIGS. 5A through 5C are diagrams illustrating a configuration of asemiconductor device according to a second modification.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

A semiconductor device 100 according to a first embodiment will bedescribed below. The semiconductor device 100 generates (emits) ordetects terahertz waves (electromagnetic waves in a frequency region ofat least 30 GHz and not more than 30 THz) of a frequency (resonancefrequency, oscillation frequency) f_(THz). Note that an example wherethe semiconductor device 100 is used as an oscillator will be describedbelow. The length of each configuration in the stacking direction of thesemiconductor device 100 will be referred to as “thickness” or “height”.

Description Regarding Circuit Configuration of Semiconductor Device

First, a circuit configuration of the semiconductor device 100 will bedescribed. FIG. 1A is a diagram describing an equivalent circuit of thesemiconductor device 100. FIG. 1C is a diagram describing an equivalentcircuit of bias circuits V_(a) and V_(b) that the semiconductor device100 has.

The semiconductor device 100 has an antenna array where a plurality ofantennas are provided. The semiconductor device 100 has an antenna arraywhere an antenna 100 a and an antenna 100 b are provided adjacently inthe present embodiment. The antenna 100 a serves both as a resonatorthat resonates with terahertz waves, and as a radiator that transmits orreceives terahertz waves. The antenna 100 a internally has asemiconductor layer 115 a for generating or detecting terahertz waves(electromagnetic waves). The antenna 100 b has the same configuration asthe antenna 100 a. The configuration of the antenna 100 a will bedescribed in detail below, and detailed description of components of theantenna 100 b that are the same as those of the antenna 100 a will beomitted.

Description will be made regarding the semiconductor device 100 providedwith two antennas in the present embodiment, but the number of antennasmay be three or more. For example, the semiconductor device 100 may havean array where the antennas are arrayed in a 3×3 matrix array.Alternately, the semiconductor device 100 may have a linear array wherethree antennas are linearly arrayed in the column or row direction. Thesemiconductor device 100 may have a configuration of an antenna arraywhere m×n (m≥2, n≥2) antennas are arrayed in a matrix. These antennasalso preferably are laid out at a pitch that is an integer multiple ofthe wavelength of terahertz waves of a frequency f_(THz).

Note that in the following description, alphabet characters indicatingthe corresponding antenna are appended to the end of the symbolsdenoting the components belonging to the antenna 100 a and the antenna100 b. More specifically, “a” is appended to the end of symbols denotingcomponents that the antenna 100 a has, and “b” is appended to the end ofsymbols denoting components that the antenna 100 b has.

As illustrated in FIG. 1A, a semiconductor 102 a, a resistor R_(a)determined by antenna radiation and conductor loss, and LC component(capacitor C_(a) and inductance L_(a)) determined by structure, areconnected in parallel in the antenna 100 a. Also, a bias circuit V_(a)for supplying bias signals to the semiconductor 102 a is connected inparallel to the semiconductor 102 a.

The semiconductor 102 a has electromagnetic-wave gain or carriernonlinearity (nonlinearity in current in accordance with voltage changein current-voltage characteristics) with regard to terahertz waves. Aresonant tunneling diode (RTD), which is a typical semiconductor havingelectromagnetic-wave gain at the terahertz wave frequency band, is usedas the semiconductor 102 a in the present embodiment. The semiconductor102 a includes a circuit where the negative differential resistance ofthe RTD and the diode capacitor are connected in parallel (omitted fromillustration).

The antenna 100 b is configured of a circuit where a semiconductor 102b, a resistor R_(b), LC component (C_(b) and L_(b)), and bias circuitV_(b) are connected in parallel, in the same way as with the antenna 100a. The antennas singularly transmit or receive terahertz waves of afrequency f_(THz).

The bias circuits V_(a) and V_(b) have a power source and stabilizationcircuit for supplying bias signals to the semiconductor 102 a of theantenna 100 a and the semiconductor 102 b of the antenna 100 b. The biascircuits V_(a) and V_(b) each have a shunt resistor 121, wiring 122, apower source 123, and a capacitor 124, as illustrated in FIG. 1C.

The shunt resistor 121 is connected in parallel with the semiconductors102 a and 102 b. The capacitor 124 is connected in parallel with theshunt resistor 121. The power source 123 supplies current necessary todrive the semiconductors 102 a and 102 b, and adjusts bias signalsapplied to the semiconductors 102 a and 102 b. In a case of using RTDsfor the semiconductors 102 a and 102 b, the bias signals are selectedfrom voltage in the negative differential resistance region of the RTDs.The shunt resistor 121 and capacitor 124 of the bias circuits V_(a) andV_(b) suppress parasitic oscillation of relatively low-frequencyresonance frequency (typically a frequency band from DC to 10 GHz) dueto the bias circuits V_(a) and V_(b).

The adjacent antenna 100 a and antenna 100 b are mutually joined by acoupling line 109. The coupling line 109 is connected to a shunt device130 connected in parallel to each of the semiconductors 102 a and 102 b.Thus, frequencies other than the operating frequency f_(THz) of theterahertz waves desired are short-circuited due to the shunt device 130being provided, and the semiconductor device 100 is low impedance atthis frequency. This suppresses resonance at a plurality of frequencybands (multimode resonance) from occurring. Note that from theperspective of antenna radiation efficiency, the shunt device 130preferably is positioned (connected) to the node of the electric fieldof terahertz waves of the standing resonance frequency f_(THz) at thecoupling line 109. The “position that is the node of the electric fieldof terahertz waves of the standing resonance frequency f_(THz) at thecoupling line 109” here is, for example, a position where the intensityof the electric field of terahertz waves of the standing resonancefrequency f_(THz) at the coupling line 109 drops by around one digit orso.

A resistor R_(c) and a capacitor C_(c) are serially connected at theshunt device 130, as illustrated in FIG. 1A. A value that is equal to orsomewhat lower than the absolute value of the combined negativedifferential resistance of the semiconductors 102 a and 102 b connectedin parallel is selected here for the resistor R_(c). Also, the capacitorC_(c) is set so that the impedance is equal to or somewhat lower thanthe absolute value of the combined negative differential resistance ofthe semiconductors 102 a and 102 b connected in parallel. That is tosay, the values of the resistor R_(c) and the capacitor C_(c) are eachpreferably set so that the impedance is lower than the absolute value ofthe negative resistance (impedance) corresponding to the gain of thesemiconductor 102 a and the semiconductor 102 b. Considering that thetypical value of negative resistance of RTDs used in terahertz bands is0.1 to 1000Ω, the value of the resistor R_(c) is set in the range of 0.1to 1000Ω. Also, the value of the capacitor C_(c) is typically set in therange of 0.1 to 1000 pF, in order to obtain a shunt effect at thefrequency range of 10 GHz to 1000 GHz. Note that it is sufficient forthe impedance conditions of the resistor R_(c) and the capacitor C_(c)with regard to the negative resistance of the RTD to be satisfied at afrequency band lower than the resonance frequency f_(THz).

Description Regarding Structure of Semiconductor Device

Next, a specific structure of the semiconductor device 100 will bedescribed. FIG. 2A is a top view of the semiconductor device 100. FIG.2B is a cross-sectional view of the semiconductor device 100 in FIG. 2A,taken along A-A′, and FIG. 2C is a cross-sectional view of thesemiconductor device 100 in FIG. 2A, taken along B-B′.

The antenna 100 a includes a substrate 113, a first conductor layer 106,a semiconductor layer 115 a, an electrode 116 a, a conductor 117 a, adielectric layer 104, and a second conductor layer 103 a. The antenna100 a has a configuration where the two conductors, i.e., the firstconductor layer 106 and the second conductor layer 103 a, sandwich thedielectric layer 104 that is made up of the three layers of a firstdielectric layer 1041, a second dielectric layer 1042, and a thirddielectric layer 1043, as illustrated in FIG. 2B. Such a configurationis known as a microstrip antenna. An example will be described in thepresent embodiment where the antennas 100 a and 100 b are used as patchantennas, which are representative microstrip resonators.

The second conductor layer 103 a is a patch conductor of the antenna 100a, and is disposed facing the first conductor layer 106 across thedielectric layer 104 (semiconductor layer 115 a). The second conductorlayer 103 a is electrically connected to the semiconductor layer 115 a.The antenna 100 a is designed as a resonator where the width of thesecond conductor layer 103 a is λ_(THz)/2 in the A-A′ direction(resonance direction). Also, the first conductor layer 106 is a groundconductor, and is electrically grounded. Note that λ_(THz) is theeffective wavelength of the dielectric layer 104 of terahertz wavesresonating at the antenna 100 a, and is expressed as λ_(THz)=λ₀×ε_(r)^(−1/2), where λ₀ represents the wavelength of the terahertz waves in avacuum, and ε_(r) represents the effective relative dielectric constantof the dielectric layer 104.

The semiconductor layer 115 a corresponds to the semiconductor 102 a inthe equivalent circuit illustrated in FIG. 1A, and includes an activelayer 101 a configured of a semiconductor that has electromagnetic-wavegain or carrier nonlinearity with respect to terahertz waves. An exampleof using an RTD as the active layer 101 a will be described in thepresent embodiment. In the following, the active layer 101 a will bedescribed as RTD 101 a.

The semiconductor layer 115 a is formed disposed on the first conductorlayer 106 that is formed on the substrate 113, with the semiconductorlayer 115 a and the first conductor layer 106 being electricallyconnected. Note that a low-resistance connection between thesemiconductor layer 115 a and the first conductor layer 106 ispreferable, to reduce Ohmic loss.

The RTD 101 a has a resonant tunneling structure layer that includes aplurality of tunnel-barrier layers. Quantum-well layers are providedbetween the plurality of tunnel-barrier layers in the RTD 101 a, therebybeing provided with a multiple quantum-well structure that generatesterahertz waves by carrier intersubband transition. The RTD 101 a haselectromagnetic-wave gain in the frequency region of terahertz wavesbased on the photo-assisted tunneling phenomenon, in the negativedifferential resistance region of current-voltage characteristics, andexhibits self-excitation oscillation in the negative differentialresistance region. The RTD 101 a is disposed at a position shifted by40% in the resonance direction (i.e., A-A′ direction) from the center ofgravity of the second conductor layer 103 a.

The antenna 100 a is an active antenna where the semiconductor layer 115a including the RTD 101 a and a patch antenna have been integrated. Thefrequency f_(THz) of terahertz waves emitted from the singular antenna100 a is determined as a resonance frequency of the entire parallelresonance circuit where the patch antenna and the semiconductor layer115 a reactance are combined. Specifically, with regard to an equivalentcircuit of the oscillator described in “Jpn. J. Appl. Phys., Vol. 47,No. 6 (2008), pp. 4375-4384”, a frequency that satisfies the amplitudecondition of Expression (1) and the phase condition of Expression (2) isdetermined as the resonance frequency f_(THz) of a resonance circuitwhere the admittance of the RTD and antenna (Y_(RTD) and Y_(aa)) arecombined.

Re[Y _(RTD)]+Re[Y _(aa)]≤0   (1)

Im[Y _(RTD)]+Im[Y _(aa)]=0   (2)

Here, Y_(RTD) represents the admittance of the semiconductor layer 115a, Re represents the real part, and Im represents the imaginary part.The semiconductor layer 115 a includes the RTD 101 a that is a negativeresistance element as the active layer, so Re[Y_(RTD)] has a negativevalue. Also, Y_(aa) represents the entire admittance of the antenna 100a as viewed from the semiconductor layer 115 a. Accordingly, thecomponents R_(a), C_(a), and L_(a) of the antenna in the equivalentcircuit in FIG. 1A are primary circuit elements for Y_(aa), and thenegative differential resistance and the diode capacitor of thesemiconductor 102 a are primary circuit elements for Y_(RTD).

Note that a quantum cascade laser (QCL) structure that has asemiconductor multilayer structure with several hundred to severalthousand of layers may be used as another example of the active layer101 a. In this case, the semiconductor layer 115 a is a semiconductorlayer including a QCL structure. Also, a negative resistance elementsuch as a Gunn diode or an IMPATT diode often used in milliwave bandsmay be used as the active layer 101 a. Also, high-frequency devices suchas a transistor with one end terminated may be used as the active layer101 a, suitable examples of which include heterojunction bipolartransistors (HBT), compound semiconductor field-effect transistors(FET), high-electron-mobility transistors (HEMT), and so forth. Also,negative differential resistance of Josephson devices that usesuperconductors may be used as the active layer 101 a.

The dielectric layer 104 is formed between the first conductor layer 106and the second conductor layer 103 a. It is demanded of the dielectriclayer 104 to be capable of being formed as a thick film (typically, athick film of at least 3 μm), to exhibit low loss and low dielectricconstant at the terahertz band, and to have good microfabricationcharacteristics (workability by planarization and etching). Inmicrostrip resonators such as patch antennas, conductor loss is reducedand radiation efficiency can be improved by forming the dielectric layer104 thicker. Now, the thicker the dielectric layer 104 is, the betterthe radiation efficiency of the resonator is, but multimode resonanceoccurs if excessively thick. Accordingly, the thickness of thedielectric layer 104 preferably is in a range of not more than 1/10 ofthe oscillation wavelength.

Meanwhile, miniaturization and high current density of diodes isrequired to realize high frequencies and high output of oscillators.Accordingly, measures such as suppressing leak current and migration isdemanded of the dielectric layer 104, with regard to the insulationstructure of the diode. In the present invention, for this reason, thedielectric layer 104 includes two dielectric layers of different typesof materials (first dielectric layer 1041 and second dielectric layer1042).

For the first dielectric layer 1041, organic dielectric materials suchas benzocyclobutene (BCB, manufactured by The Dow Chemical Company,ε_(r1)=2), polytetrafluoroethylene, polyimide, and so forth, can besuitably used. Note that ε_(r1) is the relative dielectric constant ofthe first dielectric layer 1041. Also, inorganic dielectric materialssuch as tetraethyl orthosilicate (TEOS) oxide films, spin-on glass, orthe like, which are suitable for relatively thick film formation andhave a low dielectric constant, may be used for the first dielectriclayer 1041.

It is demanded of the second dielectric layer 1042 to exhibit insulatingproperties (nature of behaving as an insulator or a high-value resistorthat does not allow electricity to pass under DC voltage), barrierproperties (nature of preventing diffusion of metal materials used forelectrodes), and workability (nature allowing precise working insubmicron order). Inorganic insulator materials, such as silicon oxide(ε_(r2)=4), silicon nitride (ε_(r2)=7), aluminum oxide, aluminumnitride, and so forth, can be suitably used as the second dielectriclayer 1042 to satisfy these properties. Note that ε_(r2) is the relativedielectric constant of the second dielectric layer 1042.

The third dielectric layer 1043 will be described later. Note that in acase where the dielectric layer 104 is a three-layer structure as in thepresent embodiment, the relative dielectric constant ε_(r) of thedielectric layer 104 is an effective relative dielectric constantdetermined from the thickness and relative dielectric constant of eachof the first dielectric layer 1041 through third dielectric layer 1043.Also, the dielectric layer 104 does not have to be a three-layerstructure in the semiconductor device 100, and may be a structure of onelayer only.

Also, from the perspective of impedance matching of antenna and air(space), the difference in the dielectric constant between the antennaand air preferably is maximally small. Accordingly, a different materialfrom the second dielectric layer 1042 is preferably used for the firstdielectric layer 1041, preferably a material that has a lower relativedielectric constant than the second dielectric layer 1042(ε_(r1)<ε_(r2)).

The electrode 116 a is disposed on the opposite side of thesemiconductor layer 115 a from the side where the first conductor layer106 is disposed. The electrode 116 a and the semiconductor layer 115 aare electrically connected. The semiconductor layer 115 a and theelectrode 116 a are embedded in the second dielectric layer 1042 (seconddielectric layer 1042 and third dielectric layer 1043). Morespecifically, the perimeters of the semiconductor layer 115 a and theelectrode 116 a are covered by the second dielectric layer 1042 (seconddielectric layer 1042 and third dielectric layer 1043).

The electrode 116 a is suitable for reduction in Ohmic loss and RC delaydue to serial resistance, as long as the electrode 116 a is a conductorlayer in Ohmic connection with the semiconductor layer 115 a. In a casewhere the electrode 116 a is used as an Ohmic electrode, examples ofmaterials suitably used for the electrode 116 a include Ti/Pd/Au,Ti/Pt/Au, AuGe/Ni/Au, TiW, Mo, ErAs, and so forth.

Also, if the region of the semiconductor layer 115 a in contact with theelectrode 116 a is a semiconductor doped with an impurity at a highconcentration, contact resistance can be further reduced, which issuitable for realizing high output and high frequencies. The absolutevalue of the negative resistance indicating the magnitude of gain of theRTD 101 a used in the terahertz waveband is generally in the order of 1to 100Ω, so the loss of electromagnetic waves is preferably kept to notmore than 1% thereof. Accordingly, the contact resistance at the Ohmicelectrode preferably is suppressed to not more than 1Ω, as a generalguide.

Also, in order to operate in the terahertz band, the width of thesemiconductor layer 115 a (≈electrode 116 a) is around 0.1 to 5 μm as atypical value. Accordingly, the resistivity is kept to not more than 10Ω·μm², suppressing the contact resistance to a range of 0.001 to severalΩ. As another form, a metal that exhibits Schottky contact rather thanOhmic contact may be used for the electrode 116 a. In this case, thecontact interface between the electrode 116 a and the semiconductorlayer 115 a exhibits rectifying properties, making for a suitableconfiguration for the antenna 100 a as a terahertz wave detector. Notethat a configuration where an Ohmic electrode is used as the electrode116 a will be described in the present embodiment.

In the stacking direction of the RTD 101 a, the first conductor layer106, the semiconductor layer 115 a, the electrode 116 a, the conductor117 a, and the second conductor layer 103 a are stacked in that orderfrom the substrate 113 side, as illustrated in FIG. 2B.

The conductor 117 a is formed inside the dielectric layer 104, and thesecond conductor layer 103 a and the electrode 116 a are electricallyconnected via the conductor 117 a. Now, if the width of the conductor117 a is excessively great, radiation efficiency deteriorates due todeterioration in resonance characteristics of the antenna 100 a andincrease parasitic capacitance. Accordingly, the width of the conductor117 a preferably is a dimension of a level where there is nointerference with the resonance electric field, and typically, not morethan λ/10 is suitable. Also, the width of the conductor 117 a can bereduced to a level where serial resistance is not increased, and can bereduced to around twice the skin depth as a general guide. Accordingly,taking into consideration reduction of the serial resistance to a levelaround not more than 1Ω, the width of the conductor 117 a typically isin a range of at least 0.1 μm and not more than 20 μm, as a generalguide.

A structure that electrically connects between upper and lower layers,such as the conductor 117 a, is referred to as a via. The firstconductor layer 106 and the second conductor layer 103 a serve as, inaddition to roles as members making up a patch antenna, electrodes forinjecting current to the RTD 101 a by being connected to the via. Amaterial having resistivity not greater than 1×10⁻⁶ Ω·m is preferablefor the material of the conductor 117 a. Specifically, metals andmetal-containing compounds such as Ag, Au, Cu, W, Ni, Cr, Ti, Al, AuInalloy, TiN, and so forth are suitably used as materials for theconductor 117 a.

The second conductor layer 103 a is connected to lines 108 a 1 and 108 a2. The lines 108 a 1 and 108 a 2 are leads connected to bias linesincluding the bias circuit V_(a). The width of the lines 108 a 1 and 108a 2 is set to be narrower than the width of the second conductor layer103 a. Note that width here is the width in the resonance direction ofelectromagnetic waves in the antenna 100 a (i.e., the A-A′ direction).For example, the width of the lines 108 a 1 and 108 a 2 suitably is notmore than 1/10 of the effective wavelength λ of terahertz waves of thestanding resonance frequency f_(THz) in the antenna 100 a (not more thanλ/10). The reason for this is that the lines 108 a 1 and 108 a 2 arepreferably disposed with dimensions and positions such that do notinterfere with the resonance electric field in the antenna 100 a, fromthe perspective of improved radiation efficiency.

Also, the positions of the lines 108 a 1 and 108 a 2 are preferably atnodes of the electric field of the resonance frequency f_(THz) terahertzwaves standing in the antenna 100 a. The lines 108 a 1 and 108 a 2 herehave a configuration where impedance is sufficiently higher than theabsolute value of the negative differential resistance of the RTD 101 aat the frequency band near the resonance frequency f_(THz). In otherwords, the lines 108 a 1 and 108 a 2 are connected to the antenna so asto have high impedance as viewed from the RTD at the resonance frequencyf_(THz). In this case, the antennas of the semiconductor device 100(antennas other than the antenna 100 a) and the antenna 100 a areisolated at the frequency f_(THz) with regard to routes via bias linesincluding the lines 108 a 1 and 108 a 2 and the bias circuit V_(a). Thissuppresses current of the resonance frequency f_(THz) induced at eachantenna from acting on (affecting) other adjacent antennas via biaslines. This is a configuration that also suppresses interference betweenthe electric field of the resonance frequency f_(THz) standing in theantenna 100 a and the power supply members thereof.

The bias circuits V_(a) and V_(b) each include the shunt resistor 121,the wiring 122, the power source 123, and the capacitor 124. The wiring122 invariably has a parasitic inductance component, and accordingly isillustrated as an inductor in FIG. 1C. The power source 123 suppliesbias signals necessary for driving the RTD 101 a and RTD 101 b. Thevoltage of the bias signals is typically selected from the voltage ofthe negative differential resistance region of the RTDs used as the RTDs101 a and 101 b. In the case of the antenna 100 a, the bias voltage fromthe bias circuits V_(a) and V_(b) is supplied to the RTD 101 a withinthe antenna 100 a via the lines 108 a 1 and 108 a 2.

Now, the shunt resistor 121 and the capacitor 124 of the bias circuitsV_(a) and V_(b) serve to suppress parasitic oscillation of arelatively-low frequency resonance frequency (typically a frequency bandfrom DC to 10 GHz) due to the bias circuits V_(a) and V_(b). A valuethat is equal to or somewhat lower than the absolute value of thecombined negative differential resistance of the RTDs 101 a and 101 bconnected in parallel is selected for the value of the shunt resistor121. The capacitor 124 is also set so that impedance is equal to orsomewhat lower than the absolute value of the combined negativedifferential resistance of the RTDs 101 a and 101 b connected inparallel, in the same way as with the shunt resistor 121. That is tosay, the bias circuits V_(a) and V_(b) are set so that the impedance islower than the absolute value of the combined negative resistancescorresponding to the gain at the DC to 10 GHz frequency band by thesesshunt elements. Generally, the capacitor 124 is preferably greaterwithin the above-described range, and capacitance in the order of tensof pF is used in the present embodiment. The capacitor 124 is adecoupling capacitor. A metal-insulator-metal (MIM) structure sharingthe substrate with the antenna 100 a may be used, for example.

Description Regarding Antenna Array

The semiconductor device 100 has an antenna array where the two antennas100 a and 100 b are E-plane coupled. The antennas singularly emitterahertz waves of the frequency f_(THz). The adjacent antennas aremutually coupled by the coupling line 109, and are mutuallyinjection-locked at the resonance frequency f_(THz) of terahertz waves.

Now, being mutually injection-locked means that all of a plurality ofself-excitation oscillators are oscillating in a frequency-locked statedue to mutual interaction. For example, the antenna 100 a and theantenna 100 b are mutually coupled by the coupling line 109. Note that“mutually coupled” refers to a phenomenon where a current induced at acertain antenna acts upon another adjacent antenna, and changes thetransmission/reception characteristics of each other. Locking ofmutually-coupled antennas at the same phase or opposite phase causes theelectric field between the antennas to be strengthened or weakened bythe mutual injection-locking phenomena, whereby increase/decrease inantenna gain can be adjusted.

Oscillation conditions of the semiconductor device 100 having theantenna array can be determined according to mutual injection lockingconditions in a configuration where two or more individual RTDoscillators are coupled, disclosed in “J. Appl. Phys., Vol. 103, 124514(2008)”. Specifically, oscillation conditions for the antenna arraywhere the antenna 100 a and the antenna 100 b are coupled by thecoupling line 109 will be considered. At this time, two oscillationmodes of inphase mutual-injection locking and antiphase mutual-injectionlocking occur. Oscillation conditions for the oscillation mode ofinphase mutual-injection locking (even mode) are represented inExpressions (3) and (4), and oscillation conditions for the oscillationmode of antiphase mutual-injection locking (odd mode) are represented inExpressions (5) and (6).

Inphase (even mode): frequency f=f_(even)

Y _(even) =Y _(aa) +Y _(ab) +Y _(RTD)

Re(Y _(even))≤0   (3)

Im(Y _(even))=0   (4)

Antiphase (odd mode): frequency f=f_(odd)

Y _(odd) =Y _(aa) +Y _(ab) +Y _(RTD)

Re(Y _(odd))≤0   (5)

Im(Y _(odd))=0   (6)

Y_(ab) is the mutual admittance between the antenna 100 a and theantenna 100 b here. Y_(ab) is proportionate to a coupling constantrepresenting the strength of coupling between the antennas, and ideally,the real part of −Y_(ab) is large and the imaginary part preferably iszero. The semiconductor device 100 according to the present embodimentis coupled under conditions of inphase mutual-injection locking, wherethe resonance frequency f_(THz)≈f_(even). Other antennas are alsocoupled under conditions of the above-described inphase mutual-injectionlocking by the coupling line 109 between the antennas, in the same way.

The coupling line 109 is made up of a microstripline that has astructure where the dielectric layer 104 is sandwiched between a thirdconductor layer 110 stacked on the dielectric layer 104, and the firstconductor layer 106. The antennas are coupled by DC coupling in thesemiconductor device 100. In order to mutually lock the antennas witheach other at the resonance frequency f_(THz), the third conductor layer110 (the top conductor of the coupling line 109 that couples the antenna100 a and the antenna 100 b) is directly connected to the secondconductor layer 103 a and the second conductor layer 103 b. The thirdconductor layer 110 and the second conductor layers 103 a and 103 b areformed in the same layer in the semiconductor device 100.

The antenna 100 a and the adjacent antenna 100 b are mutually coupled bythe structure having such a coupling line 109, and operate mutuallylocked at the oscillated terahertz wave frequency f_(THz). The antennaarray locked by DC coupling can lock among adjacent antennas by strongcoupling, and accordingly locking operations by frequency lockingreadily occur, and variance in frequency and phase among the antennasdoes not readily occur.

The shunt device 130 is disposed (connected) at the center of thecoupling line 109 in the semiconductor device 100. The shunt device 130and the coupling line 109 are connected through a via 114. Specifically,the third conductor layer 110 of the coupling line 109 and a conductorlayer 111 that connects to the shunt device 130 are connected throughthe via 114 formed inside the first dielectric layer 1041. The via 114is connected to the third conductor layer 110 at a node of thehigh-frequency electric field of the resonance frequency f_(THz)standing in the coupling line 109. That is to say, it can be said thatthe shunt device 130 is connected to the coupling line 109 at the nodeof the high-frequency electric field of the resonance frequency f_(THz)standing in the coupling line 109. The shunt device 130 connected inthis way causes frequencies other than the resonance frequency f_(THz)of the terahertz waves to be short-circuited, and the semiconductordevice 100 has low impedance at this frequency, whereby occurrence ofmultimode resonance can be suppressed.

The conductor layer 111 is an electrode stacked on the second dielectriclayer 1042 and is connected to resistor layers 1191 and 1192 stacked onthe second dielectric layer 1042. The resistor R_(c) of the shunt device130 in the equivalent circuit illustrated in FIG. 1A is formed by theresistor layers 1191 and 1192. The resistor layers 1191 and 1192 areconnected to conductor layers 1121 and 1122 stacked on the seconddielectric layer 1042. The conductor layers 1121 and 1122 are connectedto fourth conductor layers 1181 and 1182 stacked on the third dielectriclayer 1043 through vias 1071 and 1072. The fourth conductor layers 1181and 1182 are formed in a layer between the first conductor layer 106 andthe second conductor layers 103 a and 103 b. Capacitor C_(c) of theshunt device 130 in the equivalent circuit illustrated in FIG. 1A isformed by a MIM capacitor structure where the third dielectric layer1043, which is part of the dielectric layer 104, is sandwiched betweenthe fourth conductor layers 1181 and 1182 and the first conductor layer106.

Also, there is demand for miniaturization of the resistor R_(c), torealize integration of the antenna array. Accordingly, thin films ofW—Ti (0.2 μm thick), that have a high relative resistivity and highmelting point, with resistivity of 0.7 Ω·μm, are used as the resistorlayers 1191 and 1192 in the present embodiment.

The shunt device 130 of the semiconductor device 100 includes two shuntdevices. One is a shunt device where a resistor made up of the resistorlayer 1191, and capacitor where the third dielectric layer 1043 issandwiched between the fourth conductor layer 1181 and the firstconductor layer 106, are serially connected. The other is a shunt devicewhere a resistor made up of the resistor layer 1192, and capacitor wherethe third dielectric layer 1043 is sandwiched between the fourthconductor layer 1182 and the first conductor layer 106, are seriallyconnected. Note that the values of the resistor R_(c) and capacitorC_(c) can be set to be within the above-described range by appropriatelydesigning the materials, dimensions, and structures of the shuntdevices. Now, if the width of the via 114 is excessively great,deterioration in resonance characteristics of the high-frequencyelectric field of f_(THz) propagated over the coupling line, anddeterioration of radiation efficiency due to conductor loss, occur inthe same way as with the width of the conductors 117 a and 117 b.Accordingly, the width of the via 114 preferably is a dimension of alevel where there is no interference with the resonance electric field,and typically, not more than λ/10 is suitable.

The three dielectric layers of the first dielectric layer 1041, thesecond dielectric layer 1042, and the third dielectric layer 1043, areused as the dielectric layer 104 in the semiconductor device 100. Thethird dielectric layer 1043 is used as the dielectric member for thecapacitor C_(c) of the shunt device 130, and accordingly silicon nitridewith a relatively high dielectric constant (ε_(r3)=7) is used forreduction in size of the MIM capacitor structure. Note that ε_(r3) isthe relative dielectric constant of the third dielectric layer 1043. Ina case where the dielectric layer 104 has a three-layer configuration asin the present embodiment, the effective relative dielectric constant isdetermined taking into consideration the thickness and relativedielectric constant of the third dielectric layer 1043 as well.

Description Regarding Comparison with Conventional Semiconductor Device

FIG. 3 illustrates comparison of results of analyzing the impedance ofthe semiconductor device 100 according to the present embodiment, andthe impedance of a conventional semiconductor device that does not havethe shunt device 130. Analysis was performed using HFSS, which is afinite element method high-frequency electromagnetic field solvermanufactured by ANSYS, Inc. Impedance Z here is equivalent to theinverse of Y_(aa) that is the admittance of the entire structure of theantenna 100 a. Also, Z_w/_shunt is impedance Z in a case of having theshunt device 130 as in the present embodiment. Z_w/o_shunt is impedanceZ in a case of not having the shunt device 130, as in a conventionalarrangement. Re and Im represent the real part and imaginary part,respectively, and resonance occurs at a frequency where the impedance ofthe imaginary part is 0.

A multipeak occurs in the impedance of the conventional structure, asillustrated in FIG. 3, and there is a possibility that resonance modesare occurring at the two frequency bands of near 0.42 THz and near 0.52THz. In contrast with this, there is only a single peak at the desiredresonance frequency f_(THz)=0.48 THz in the impedance of thesemiconductor device 100 according to the present embodiment, andmultimode is suppressed. The semiconductor device 100 according to thepresent embodiment has effects of suppressing occurrence of resonance atlow frequency bands (not higher than 0.1 THz) outside of the range ofthe graph illustrated in FIG. 3, due to the shunt device 130.

The shunt device 130 is disposed parallel to the RTD at the couplingline 109 in the semiconductor device 100. This suppresses multimoderesonance at frequency bands of relatively high frequency (typicallyfrom 10 GHz to 1000 GHz), and enables just resonance of operatingfrequency f_(THz) of the desired terahertz waves to be selectivelystabilized. Also, impedance change due to structure does not readilyoccur in the semiconductor device 100 according to the presentembodiment in comparison with a configuration where the antennas areserially connected by a resistor, and variance in phase and frequencydoes not readily occur.

Thus, according to the present embodiment, single-mode operation at theterahertz-wave operating frequency f_(THz) can be performed even if thenumber of antennas in the antenna array is increased. Accordingly, theupper limit of the number of antennas that can be arrayed can be raised,and effects of marked improvement can be anticipated in directionalityand frontal intensity in accordance with the increase in the number ofantennas in the array. Thus, according to the present embodiment, asemiconductor device that can realize efficient generation or detectionof terahertz waves can be provided.

Note that the shunt device is not limited to an arrangement having theresistor R_(c) and capacitor C_(c) illustrated in FIG. 1A. For example,the shunt device 130 may be configured from just resistor R_(c)connected in parallel to the semiconductors 102 a and 102 b, asillustrated in FIG. 1B.

First Modification

A semiconductor device 200 according to a first modification will bedescribed below. FIGS. 4A through 4C illustrate the semiconductor device200 according to the first modification. The semiconductor device 200has an antenna array where two antennas 200 a and 200 b are H-planecoupled. The semiconductor device 200 has an antenna array of aconfiguration where the antennas are coupled by AC coupling (capacitivecoupling). Detailed description of parts of the configurations andstructures of the antennas 200 a and 200 b that are the same as those ofthe antennas 100a and 100 b in the semiconductor device 100 will beomitted.

A coupling line 209 is made up of a microstripline that has a structurewhere a dielectric layer 204 and a fourth dielectric layer 2044 aresandwiched between a third conductor layer 210 and a first conductorlayer 206, as illustrated in FIG. 4B. The dielectric layer 204 is madeup of a first dielectric layer 2041, a second dielectric layer 2042, anda third dielectric layer 2043. Second conductor layers 203 a and 203 bare formed in a layer between the third conductor layer 210 and thefirst conductor layer 206. The third conductor layer 210 that is theupper conductor of the coupling line 209 that couples the antennas 200 aand 200 b overlaps the second conductor layers 203 a and 203 b by alength x=5 μm near the radiating ends as viewed from the stackingdirection (in planar view). At this overlapping portion, the secondconductor layers 203 a and 203 b, the fourth dielectric layer 2044, andthe third conductor layer 210 are stacked in that order. Accordingly, ametal-insulator metal (MIM) capacitor structure, where the secondconductor layers 203 a and 203 b and the third conductor layer 210sandwich the fourth dielectric layer 2044 is formed. Note that betweenthe second conductor layer 203 a and the second conductor layer 203 b isopen regarding DC, and the magnitude of coupling at low-frequencyregions lower than the resonance frequency f_(THz) is small, sointer-device isolation is secured. Meanwhile, the magnitude ofinter-antenna coupling at the resonance frequency f_(THz) band can beadjusted by capacitance.

In the semiconductor device 200, shunt devices 2301 and 2302 areconnected to the coupling line 209. The shunt devices 2301 and 2302 areconnected to the coupling line 209 through vias 2141 and 2142. The vias2141 and 2142 are connected to the third conductor layer 210 at a nodeof the high-frequency electric field of the resonance frequency f_(THz)standing in the coupling line 209. This enables frequencies other thanthe resonance frequency f_(THz) of the terahertz waves to beshort-circuited, and accordingly occurrence of multimode resonance canbe suppressed.

The third conductor layer 210 of the coupling line 209 is connected toresistor layers 2191 and 2192 stacked on the first dielectric layer 2041through the vias 2141 and 2142 formed inside the fourth dielectric layer2044. Also, the resistor layers 2191 and 2192 are connected to fourthconductor layers 2181 and 2182 stacked on the third dielectric layer2043 through vias 2071 and 2072 formed inside the first dielectric layer2041.

An MIM capacitor structure where the third dielectric layer 2043 issandwiched between the fourth conductor layers 2181 and 2182 and thefirst conductor layer 206 is formed. Such an AC coupling structure canweaken coupling among antennas, thereby suppressing transmission lossamong antennas, and improved radiation efficiency of the antenna arrayis anticipated. Note that the width of the vias 2071 and 2072 may beformed large in some instances, since the vias 2071 and 2072 are formedinside the first dielectric layer 2041 that is relatively thick.However, in a configuration where the vias 2071 and 2072 are disposed ata position away from the coupling line 209 as in the presentmodification, interference of the antenna with the resonance electricfield is suppressed even if the width of the vias 2071 and 2072 is large(typically not smaller than λ/10). Accordingly, improved antenna gaincan be anticipated.

Second Modification

A semiconductor device 300 according to a second modification, which isa specific example of a configuration where the shunt device illustratedin FIG. 1B is made up of a resistor alone will be described below. FIGS.5A through 5C illustrate the semiconductor device 300 according to thesecond modification. The semiconductor device 300 has an antenna arraywhere adjacent antennas are connected by a coupling line 309(microstripline) disposed between a first conductor layer 306 (groundingconductor) and second conductor layers 303 a and 303 b (patchconductors). Detailed description of the configurations and structuresof antennas 300 a and 300 b that are the same as those of the antennas100 a and 100 b in the semiconductor device 100 will be omitted.

The coupling line 309 is a microstripline having a structure where asecond dielectric layer 3042 is sandwiched between a third conductorlayer 310 (upper conductor) and the first conductor layer 306 (groundingconductor), and also serves as a resonator. The antenna 300 a has astructure where an RTD 301 a has been integrated in a complex resonatormade up of a patch antenna (an antenna made up of the first conductorlayer 306 and the second conductor layer 303 a) and half (the antenna300 a side half) of the coupling line 309. In the coupling line 309, thedirection perpendicular to the resonance direction of the antenna (i.e.,the A-A′ direction) is the longitudinal direction.

The length of the coupling line 309 and the size of the patch antennasare important parameters that determine the frequency of electromagneticwaves that each of the antennas 300 a and 300 b emit. Specifically, theresonance frequency f_(THz) of the antenna 300 a can be determined fromthe length of the second conductor layer 303 a and the length of thethird conductor layer 310 in the A-A′ direction. For example, anarrangement where half of the length of the third conductor layer 310 inthe A-A′ direction is an integer multiple of the effective wavelength ofthe desired resonance frequency, and the length of the second conductorlayer 303 a is ½ of the effective wavelength of the desired resonancefrequency, is suitable.

The bias circuits V_(a) and V_(b) are connected to lines 308 a and 308 bmade up of conductor layers stacked on a first dielectric layer 3041.The third conductor layer 310 is connected to a via 317 a. The via 317 aconnects between the second conductor layer 303 a and the RTD 301 a.

Adjacent antennas are coupled by DC coupling by the coupling line 309.For example, the antennas 300 a and 300 b are directly coupled by thethird conductor layer 310 that is the upper conductor of the couplingline 309. In order to intensify frequency locking between the antennas,the RTDs 301 a and 301 b are preferably disposed at the maximum point ofthe electric field of electromagnetic waves (resonance frequencyf_(THz)) standing in the coupling line.

Four shunt devices 3301 through 3304 are disposed in the coupling line309 in the semiconductor device 300, as a specific configuration exampleof the equivalent circuit of resistor R_(c) alone, illustrated in FIG.1B. For example, in the cross-section of the shunt device 3302illustrated in FIG. 5C, the third conductor layer 310 making up thecoupling line 309 is connected to a conductor layer 312 a 2 stacked onthe second dielectric layer 3042, via a resistor 319 a 2. The conductorlayer 312 a 2 is also connected to the first conductor layer 306 that isa grounding conductor, through a via 307 a 2 formed inside the seconddielectric layer 3042. The present modification is a simple structurewhere there is no need for integration of capacitor structures, andaccordingly the number of manufacturing steps can be reduced.

FIRST EXAMPLE

As a first example, a specific configuration of the semiconductor device100 according to the first embodiment will be described with referenceto FIGS. 2A through 2C. The semiconductor device 100 is a semiconductordevice that is capable of single-mode oscillation at the 0.45 to 0.50THz frequency band.

The RTDs 101 a and 101 b are configured with a Multiple Quantum Wellstructure of InGaAs/AlAs lattice-matched on the substrate 113 formed ofInP. RTDs of a double-barrier structure are used in the present example.The semiconductor heterostructure of the RTDs is the structure disclosedin “J Infrared Milli Terahz Waves (2014) 35:425-431”. As for measurementvalues of current-voltage characteristics of the RTDs 101 a and 101 b,the peak current density is 9 mA/μm², and negative differentialconductance per unit area is 10 mS/μm².

A mesa structure made up of the semiconductor layer 115 a including theRTD 101 a, and the electrode 116 a that is an Ohmic electrode, is formedin the antenna 100 a. In the present example, a columnar mesa structurethat is 2 μm in diameter is formed. The magnitude of the negativedifferential resistance of the RTD 101 a is approximately −30Ω per diodehere. In this case, the negative differential conductance (G_(RTD)) ofthe semiconductor layer 115 a including the RTD 101 a is estimated to beapproximately 30 mS, and the diode capacitance (C_(RTD)) of the RTD 101a is estimated to be approximately 10 fF.

The antenna 100 a is a patch antenna of a structure where the dielectriclayer 104 is sandwiched by the second conductor layer 103 a (patchconductor) and the first conductor layer 106 (grounding conductor). Thesemiconductor layer 115 a that includes the RTD 101 a inside isintegrated in the antenna 100 a. The antenna 100 a is a square patchantenna where one side of the second conductor layer 103 a is 150 μm,and the resonator length L of the antenna is 150 μm. A metal layerprimarily of an Au thin film, of which resistivity is low, is used forthe second conductor layer 103 a and the first conductor layer 106.

The dielectric layer 104 is disposed between the second conductor layer103a and the first conductor layer 106. The dielectric layer 104 is madeup of the three layers of the first dielectric layer 1041, the seconddielectric layer 1042, and the third dielectric layer 1043. The firstdielectric layer 1041 is formed of benzocyclobutene (BCB, manufacturedby The Dow Chemical Company, ε_(r1)=2), 5 μm thick. The seconddielectric layer 1042 is formed of SiO₂ (plasma CVD, ε_(r2)=4), 2 μmthick. The third dielectric layer 1043 is formed of SiN_(x) (plasma CVD,ε_(r3)=7), 0.1 μm thick. That is to say, the three dielectric layersthat the dielectric layer 104 includes are each formed (configured) ofdifferent materials in the present example.

The first conductor layer 106 is formed of a Ti/Pd/Au layer (20/20/200nm), and a semiconductor having an n+-InGaAs layer (100 nm) whereelectron density is not less than 1×10¹⁸ cm⁻³. In the first conductorlayer 106, the metal and semiconductor are connected by low-resistanceOhmic contact.

The electrode 116 a is an Ohmic electrode formed of a Ti/Pd/Au layer(20/20/200 nm). The electrode 116 a is connected by low-resistance Ohmiccontact to the semiconductor made of the n+-InGaAs layer (100 nm) whereelectron density is not less than 1×10¹⁸ cm⁻³, formed on thesemiconductor layer 115 a.

The structure of around the RTD 101 a in the stacking direction is, inorder from the substrate 113 side, the substrate 113, the firstconductor layer 106, the semiconductor layer 115 a including the RTD 101a, the electrode 116 a, the conductor 117 a, and the second conductorlayer 103 a, stacked in that order and electrically connected to eachother. The conductor 117 a is formed (configured) of a conductorcontaining Cu (copper).

The RTD 101 a is disposed at a position shifted by 40% (60 μm) in theresonance direction (i.e., A-A′ direction) from the center of gravity ofthe second conductor layer 103 a. The input impedance at the time ofsupplying high-frequency power from the RTD to the patch antenna isdetermined by the position of the RTD 101 a in the antenna 100 a. Thesecond conductor layer 103 a is connected to the lines 108 a 1 and 108 a2.

The lines 108 a 1 and 108 a 2 are formed of metal layers including Ti/Au(5/300 nm) stacked on the first dielectric layer 1041, and are connectedto the bias circuits V_(a), V_(b). The antenna 100 a is designed so thatoscillation of power of 0.2 mW is obtained at the frequency f_(THz)=0.48THz, by setting the bias to the negative resistance region of the RTD101 a. The lines 108 a 1 and 108 a 2 are configured of patterns of metallayers including Ti/Au (5/300 nm), 75 μm in length in the resonancedirection (i.e., A-A′ direction) and 10 μm in width. The lines 108 a 1and 108 a 2 are connected to the second conductor layer 103 a at thecenter of the second conductor layer 103 a in the resonance direction(i.e., A-A′ direction) and at the end in the B-B′ direction. Theconnection position corresponds to a node of the electric field off_(THz) terahertz waves standing in the antenna 100 a.

The semiconductor device 100 has an antenna array where the two antennas100 a and 100 b are arrayed in the electric field direction of radiatedelectromagnetic waves (i.e., E-plane direction) and mutually coupled.The antennas are designed to singularly emit terahertz waves of thefrequency f_(THz), and are laid out in the A-A′ direction at a pitch of340 μm. The adjacent antennas are mutually coupled by the coupling line109 including the third conductor layer 110 configured of Ti/Au (5/300nm). More specifically, the second conductor layer 103 a and the secondconductor layer 103 b are connected by the third conductor layer 110that is 5 μm in width and 190 μm in length. The antenna 100 a and theantenna 100 b are mutually injection-locked and oscillate at theresonance frequency f_(THz)=0.48 THz, in a state with the phasesmatching each other (inphase).

In the semiconductor device 100, the shunt device 130 is disposed at thecenter of the coupling line 109. The shunt device 130 and the couplingline 109 are connected through the via 114. Specifically, the thirdconductor layer 110 of the coupling line 109, and the conductor layer111, configured of Ti/Au (5/300 nm), are connected through the via 114formed of Cu inside the first dielectric layer 1041.

The via 114 is a columnar structure 10 μm in diameter and 5 μm inheight. The conductor layer 111 is connected to the resistor layers 1191and 1192 formed of W—Ti (0.2 μm thick) with resistivity of 0.7 Ω·μm. Theresistor layers 1191 and 1192 here are designed to be 20Ω each, andworked to patterns 4 μm in width and 20 μm in length.

The resistor layers 1191 and 1192 are connected to the fourth conductorlayers 1181 and 1182 through the conductor layers 1121 and 1122 and thevias 1071 and 1072. The conductor layers 1121 and 1122 and the fourthconductor layers 1181 and 1182 are formed (configured) of Ti/Au (5/300nm). The vias 1071 and 1072 are formed of Cu. The vias 1071 and 1072 arecolumnar structures 10 μm in diameter, and 2 μm in height.

The shunt device 130 where the resistor R_(c) and capacitor C_(c) areserially connected is formed by the MIM capacitor structure where thethird dielectric layer 1043 is sandwiched between the fourth conductorlayers 1181 and 1182 and the first conductor layer 106, and the resistorlayers 1191 and 1192.

The third dielectric layer 1043 is formed (configured) of siliconnitride (ε_(r3)=7), 0.1 μm thick. The fourth conductor layers 1181 and1182 are formed as rectangular patterns 50 μm in width and 60 μm inlength. Capacitance of 2 pF is formed for each MIM structure. Connectingthe shunt device 130 to the coupling line 109 as in the semiconductordevice 100 suppresses multimode resonance at frequency bands ofrelatively high frequency, and enables just the operating frequencyf_(THz) of the desired terahertz waves to be selected in a stablemanner. Note that the frequency band of the relatively high frequencytypically is 10 GHz to 1000 GHz.

Supply of electric power to the semiconductor device 100 is performedfrom the bias circuits V_(a) and V_(b), and bias voltage of negativedifferential resistance region is normally applied to supply biascurrent. In the case of the semiconductor device 100 disclosed in thepresent example, radiation of 0.4 mW terahertz electromagnetic waves isobtained at the frequency of 0.48 THz by oscillation operations in thenegative resistance region.

In this way, according to the present example, loss of electromagneticwaves can be reduced as compared with conventional arrangements, andmore efficient emission or detection of terahertz waves can be realized.

Manufacturing Method for Semiconductor Device

Next, a manufacturing method for the semiconductor device 100 accordingto the present example will be described. The semiconductor device 100is manufactured (fabricated) as follows.

(1) An InGaAs/AlAs semiconductor multilayer structure is epitaxiallygrown on the InP substrate 113, thereby forming the semiconductor layers115 a and 115 b including the RTDs 101 a and 101 b. Molecular-beamepitaxy (MBE) or metalorganic vapor-phase epitaxy (MOVPE) is used forthe epitaxial growth.

(2) Film formation of a Ti/Pd/Au layer (20/20/200 nm) is performed onthe semiconductor layers 115 a and 115 b by sputtering, thereby formingthe electrodes 116 a and 116 b.

(3) The electrodes 116 a and 116 b and the semiconductor layers 115 aand 115 b are formed into circular mesa forms 2 μm in diameter, therebyforming mesa structures. The mesa forms are formed usingphotolithography and dry etching by inductively-coupled plasma (ICP).

(4) After the first conductor layer 106 is formed on the substrate 113by the lift-off process being performed on the etched face, a film ofsilicon nitride, 0.1 μm thick, is formed by plasma CVD, thereby formingthe third dielectric layer 1043.

(5) A Ti/Au layer (5/300 nm) making up the fourth conductor layers 1181and 1182 is formed on the third dielectric layer 1043. Thus, capacitorC_(c) where the third dielectric layer 1043 is sandwiched between thefourth conductor layers 1181 and 1182 and the first conductor layer 106is formed.

(6) A film of silicon oxide, 2 μm thick, is formed by plasma CVD,thereby forming the second dielectric layer 1042.

(7) The second dielectric layer 1042 is dry-etched and via holes areformed. Once the via holes are formed, the via holes are filled in withCu and planarized, using sputtering, electroplating, andchemical-mechanical polishing, thereby forming the vias 1071 and 1072.

(8) The resistor layers 1191 and 1192 of W—Ti (0.2 μm thick) on thesecond dielectric layer 1042 are formed by sputtering and dry etching.Thus, the shunt device 130 where the capacitor C_(c) and resistor R_(c)are serially connected is formed.

(9) The conductor layers 111, 1121, and 1122, of a Ti/Au layer (5/300nm) on the second dielectric layer 1042, are formed by sputtering anddry etching.

(10) Filling in with BCB and planarization are performed using spincoating and dry etching, thereby forming the first dielectric layer1041, 5 μm thick.

(11) The BCB and silicon oxide of the portions making up the conductors117 a and 117 b and the via 114 are removed by photolithography and dryetching, forming via holes.

(12) The via holes are filled in with a conductor containing Cu, therebyforming the conductors 117 a and 117 b and the via 114. Formation of theconductors 117 a and 117 b and the via 114 is performed usingsputtering, electroplating, and chemical-mechanical polishing, therebyfilling the via holes with Cu and planarizing.

(13) A film for an electrode Ti/Au layer (5/300 nm) is formed bysputtering, thereby forming the second conductor layers 103 a and 103 band the third conductor layer 110.

(14) Photolithography and dry etching are performed byinductively-coupled plasma (ICP), thereby patterning the secondconductor layers 103 a and 103 b and the third conductor layer 110. Thisforms the coupling line 109.

(15) The shunt resistor 121 and MIM capacitor 124 are formed inside thechip, and the shunt resistor 121 and MIM capacitor 124 are connected tothe wiring 122 and the power source 123 by wire bonding or the like.Thus, the semiconductor device 100 is completed.

A preferred embodiment and example of the present invention has beendescribed above, but the present invention is not limited to theembodiment and example, and various modifications and alterations may bemade without departing from the spirit and scope thereof. For example, acase where the carriers are electrons is assumed in the description ofthe embodiment and example made above, but this is not limiting, and anarrangement may be made where holes are used. Materials for thesubstrate and dielectric members can be selected in accordance withusage, and semiconductors such as silicon, gallium arsenide, indiumarsenide, gallium phosphide, and so forth, glass, ceramics, and resinssuch as polytetrafluoroethylene, polyethylene terephthalate, and soforth, can be used. Note that the structures and materials in theembodiment and example described above can be selected as appropriate inaccordance with the desired frequency and so forth.

Further, in the above-described embodiment and example, a square patchantenna is used as the terahertz-wave resonator. However, the shape ofthe resonator is not limited to this, and a resonator of a structureusing a patch conductor that is polygonal such as rectangular ortriangular or the like, circular, elliptical, and so forth, for example,can be used.

The number of negative differential resistance devices to be integratedin the semiconductor device is not limited to one, and a resonator maybe made that has a plurality of negative differential resistancedevices. The number of lines is not limited to one, and a configurationmay be made where a plurality of lines are provided.

Also, a double-barrier RTD made of InGaAs/AlAs grown on an InP substratehas been described above for the RTD. However, these structures andmaterials are not limiting, and combinations of other structures andmaterials may be made. For example, an RTD having a triple-barrierquantum well structure, or an RTD having a multiple-barrier quantum wellstructure of fourfold or more, may be used.

Also, each of the following combinations may be used as RTD materials.

-   -   GaAs/AlGaAs and GaAs/AlAs, InGaAs/GaAs/AlAs formed on a GaAs        substrate    -   InGaAs/InAlAs, InGaAs/AlAs, InGaAs/AlGaAsSb formed on an InP        substrate    -   InAs/AlAsSb and InAs/AlSb formed on an InAs substrate    -   SiGe/SiGe formed on a Si substrate

According to the present technology, more efficient generation ordetection of terahertz waves can be realized in a device provided with aplurality of antennas.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2019-173084, filed on Sep. 24, 2019, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A device, comprising: an antenna array providedwith a plurality of antennas each having a semiconductor layer havingterahertz-wave gain; and a coupling line for mutual frequency-locking ofat least two of the antennas at a frequency of the terahertz-wave,wherein the coupling line is connected to a shunt device, and the shuntdevice is connected in parallel to the semiconductor layer of each ofthe two antennas.
 2. The device according to claim 1, wherein theplurality of antennas are each connected to a bias circuit including apower source supplying a bias signal to the semiconductor layer.
 3. Thedevice according to claim 1, wherein each of the plurality of antennasincludes: a substrate; a first conductor layer stacked on the substrate;the semiconductor layer electrically connected to the first conductorlayer; a second conductor layer electrically connected to thesemiconductor layer and facing the first conductor layer across thesemiconductor layer; and a first dielectric layer formed between thefirst conductor layer and the second conductor layer.
 4. The deviceaccording to claim 3, further comprising a third conductor layer,wherein the coupling line has a structure where the first dielectriclayer is sandwiched between the third conductor layer and the firstconductor layer.
 5. The device according to claim 4, wherein the secondconductor layer is formed in a layer between the third conductor layerand the first conductor layer, and the second conductor layer and thethird conductor layer form a capacitor by sandwiching therebetween asecond dielectric layer, which differs from the first dielectric layer.6. The device according to claim 3, wherein each of the plurality ofantennas further includes a fourth conductor layer formed in a layerbetween the first conductor layer and the second conductor layer, and inthe shunt device, a capacitor, in which a part of the first dielectriclayer is sandwiched between the fourth conductor layer and the firstconductor layer, and a resistor are serially connected.
 7. The deviceaccording to claim 1, wherein, in the shunt device, a resistor and acapacitor are serially connected.
 8. The device according to claim 7,wherein the resistor and the capacitor in the shut device are each setto an impedance lower than an impedance of the semiconductor layer in afrequency band lower than the terahertz-wave frequency.
 9. The deviceaccording to claim 1, wherein the shunt device is configured of aresistor.
 10. The device according to claim 1, wherein the shut deviceis connected to a node of an electric field of the terahertz waves inthe coupling line.
 11. The device according to claim 1, wherein theantenna array is formed to have the antennas in an m×n matrix form(where m≥2 and n≥2).
 12. The device according to claim 1, wherein theantennas are formed at a pitch of an integer multiple of a wavelength ofthe terahertz waves.
 13. The device according to claim 1, wherein theantennas are patch antennas.
 14. The device according to claim 1,wherein the semiconductor layer includes a negative resistance element.15. The device according to claim 14, wherein the negative resistanceelement is a resonant tunneling diode.
 16. The device according to claim1, wherein the terahertz waves are electromagnetic waves of a frequencyregion at at least 30 GHz and not more than 30 THz.
 17. A manufacturingmethod for a device provided with an antenna array having a plurality ofantennas, the method comprising: a step of forming, on a substrate, asemiconductor layer having terahertz-wave gain; a step of forming, onthe substrate, a first conductor layer; a step of forming a shunt deviceconnected in parallel to a semiconductor layer of each of two antennas,and connected to a coupling line for mutual frequency-locking of theplurality of antennas at the terahertz-wave frequency; and a step offorming a third conductor layer to form the coupling line that has astructure where a first dielectric layer is sandwiched between the firstconductor layer and the third conductor layer.